Hitless modulation scheme change systems and methods in optical networks

ABSTRACT

A hitless modulation change method at a node in an optical network includes determining that a modulation change is warranted for an optical modem in the node, the optical modem configured to communicate over an optical link; determining an impact of the modulation change on the optical link and associated underlying connections thereon; causing changes in a data plane for the associated underlying connections, prior to performing the modulation change; and causing the modulation change subsequent to accommodating the associated underlying connections in the data plane, thereby minimizing interruptions of the associated underlying connections due to the modulation change.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present non-provisional patent application/patent is acontinuation-in-part of U.S. patent application Ser. No. 14/176,908,filed on Feb. 10, 2014, and entitled “SYSTEMS AND METHODS FOR MANAGINGEXCESS OPTICAL CAPACITY AND MARGIN IN OPTICAL NETWORKS,” the contents ofwhich are incorporated in full by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to optical networking. Moreparticularly, the present disclosure relates to systems and methods forhitless modulation scheme changes in optical networks.

BACKGROUND OF THE DISCLOSURE

Fiber optic communication networks are experiencing rapidly increasinggrowth in capacity. This capacity growth is reflected by individualchannel data rates, scaling from 10 Gbps (gigabits per second), to 40Gbps, to developing 100 Gbps, and to future projections of 1000 Gbpschannels and beyond. The capacity growth is also reflected by increasingtotal channel count and/or optical spectrum carried within an opticalfiber. In the past, optical channels were deployed with a fixed capacityin terms of bandwidth as well as a fixed amount of overhead for forwarderror correction (FEC). For example, in a conventional systemdeployment, channels are deployed at 10 Gbps or 40 Gbps (plus associatedoverhead for FEC). These channels are designed to provide fixed datathroughput capacity of 10 Gbps or 40 Gbps. Moreover, the performancelimits of these channels are established assuming that the system isoperating at full capacity, with all the optical channels present. Thefirst in channels will operate in much more benign condition and havesignificant extra margin available. This margin is not utilized untilmuch later in the life cycle of the system. For example, a singlewavelength deployed on a new optical line system could have more than 10dB of excess margin that is not currently utilized (without adding newhardware). This un-used margin can be considered wasted and forcing thesystem to operate in a non-cost effective way. If this extra margincould be utilized, even in a temporary way, to enhance data throughputof the modem for example, the economics of the system would besignificantly improved.

Of note, next generation optical modems are equipped with the capabilityto support variable data throughput applications. Moreover, thiscapability will be provisionable. Therefore, depending on theopportunity, it would be advantageous to provision a modem at a higherdata throughput when extra margin is available on new and low channelcount deployments, usage of these next generation modem will allow tomine and use this excess margin and wasted capacity without requiringadditional hardware. However, this excess margin will disappear as thechannel counts approach full fill. It would be advantageous to havesystems and methods for managing excess optical capacity and margin inoptical networks in view of the above.

Fiber optic communication networks today are pushing up against theShannon Limit within the non-linear tolerance of the transpondertechnology currently in use. There is great interest in providing thebest spectral efficiency possible, which is leading to the developmentof adaptive modulation techniques applied to fiber optic transmission.In wireless and Digital Subscriber Loop (DSL) technology, it is quitecommon to use adaptive modulation schemes which adapt to linkconditions, e.g. High-Speed Downlink Packet Access (HSDPA) andAsymmetric digital subscriber line (ADSL2+). In optical, some latestgeneration transponders on the market are capable of changing modulationscheme, e.g. Ciena's WaveLogic3 family. Transponders in the future willbe able to change modulation scheme more quickly, and may be optimizedto do so. However, today's systems cannot take advantage of these in ahitless manner.

Although wireless and DSL technologies can react to channel conditionsusing adaptive modulation, the system constraints in fiber opticcommunication networks would not allow similar system techniques towork. In particular, there are two assumptions built into the algorithmsused in these systems for wireless and DSL technologies. First, the datawhich is transported in both cases (wireless and DSL technologies) isbursty in nature, and the actual user data throughput vs. actual bitrate can be controlled. In wireless communication, the application layeris visible to the controller. In other words, the systems are designedto allow for periodic optimization where the resulting changes can be inmodulation scheme. Optical transport networks are the core of the datanetwork and as such see a rather continuous flow of traffic due tomultiple levels of multiplexing and grooming. There are many sources ofthis data and the volume is also very high, so hold-offs on datatransmission become too complex and/or expensive to implement.

Second, another simplifying condition is that the transmission time(distance) from modulator to demodulator is small compared to the baudrate of the transmission. In practical terms, for example, for HSDPAnetworks in a 5 km cell and the baud rate of 5 Mbps, there are 8.3 baudin flight at any time. In an optical network using 100 Gbps over 2000km, there is 440 million baud in flight. This nearly 8 orders ofmagnitude difference represent a key difference in how to perform suchchanges. Although there are some transponder on the market today whichcan change the operational state to accommodate a different spectralefficiency which may be allowed by the link conditions, these cause somelength of outage which can only be managed out of service or as afailure in the system, both of which have negative effects on thesystem, and drive operational complexity for the end user. Treating itas an outage may cause higher level protocols to attempt to recover fromthe failure, leaving the system vulnerable to further failures. Thetreatment as a failure may also cause re-transmission of data, etc. Withthe vast amount of data involved, this is simply unacceptable.

For example, using conventional optical modems, such as the WaveLogic3,testing was performed to switch in-service between Quadrature PhaseShift Keying (QPSK) and 16-Quadrature Amplitude Modulation (16-QAM). Theswitch requires several seconds because operating conditions on the lineincluding non-linear impairments have to be calculated. Again, it isexpected that the switch can be optimized, but likely not on the orderof several milliseconds.

BRIEF SUMMARY OF THE DISCLOSURE

In an exemplary embodiment, a hitless modulation change method at a nodein an optical network includes determining that a modulation change iswarranted for an optical modem in the node, the optical modem configuredto communicate over an optical link; determining an impact of themodulation change on the optical link and associated underlyingconnections thereon; causing changes in a data plane for the associatedunderlying connections, prior to performing the modulation change; andcausing the modulation change subsequent to accommodating the associatedunderlying connections in the data plane, thereby minimizinginterruptions of the associated underlying connections due to themodulation change. The hitless modulation change method can furtherinclude causing reversion of the associated underlying connections tothe optical link subsequent to completion and verification of themodulation change. The causing changes in the data plane can utilize acontrol plane and restoration of the associated underlying connectionsper normal control plane behavior. The normal control plane behavior caninclude any of mesh restoration via the control plane, 1+1/1:1 AutomaticProtection Switching (APS), Subnetwork Connection Protection (SNCP),ring restoration, G.8032 Ethernet Ring Protection Switching (ERPS), andVirtual Local Area Network (VLAN) protection. The determining the impactcan include determining a length of time the modulation change willtake. The length of time the modulation change will take can be based ona type of the modulation change from first modulation scheme to a secondmodulation scheme, link conditions, and line measurements. The length oftime can be communicated with the changes in the data plane for theassociated underlying connections. The determining steps and the causingsteps can be performed by a control agent communicatively coupled to thenode. The control agent can operate in an autonomous manner andcommunicates with existing control plane functionality associated withthe node to cause the changes in the data plane.

In another exemplary embodiment, a hitless modulation change systemcommunicatively coupled to a node in an optical network includes aprocessor; and memory storing instructions that, when executed, causethe processor to determine that a modulation change is warranted for aoptical modem in the node, the optical modem is configured tocommunicate over an optical link, determine an impact of the modulationchange on the optical link and associated underlying connectionsthereon, cause changes in a data plane for the associated underlyingconnections, prior to performing the modulation change, and cause themodulation change subsequent to accommodating the associated underlyingconnections in the data plane, thereby minimizing interruptions of theassociated underlying connections due to the modulation change. Thememory storing instructions that, when executed, can further cause theprocessor to: cause reversion of the associated underlying connectionsto the optical link subsequent to completion and verification of themodulation change. The changes in the data plane can be caused utilizinga control plane and restoration of the associated underlying connectionsper normal control plane behavior. The normal control plane behavior caninclude any of mesh restoration via the control plane, 1+1/1:1 AutomaticProtection Switching (APS), Subnetwork Connection Protection (SNCP),ring restoration, G.8032 Ethernet Ring Protection Switching (ERPS), andVirtual Local Area Network (VLAN) protection. The impact can includedetermining a length of time the modulation change will take. The lengthof time the modulation change will take can be based on a type of themodulation change from first modulation scheme to a second modulationscheme, link conditions, and line measurements. The length of time canbe communicated with the changes in the data plane for the associatedunderlying connections. The hitless modulation change system can beimplemented through or communicatively coupled to a Software DefinedNetworking (SDN) controller. The control agent can operate in anautonomous manner and communicates with existing control planefunctionality associated with the node to cause the changes in the dataplane.

In a further exemplary embodiment, an optical node implementing hitlessmodulation changes in an optical network includes one or more opticalmodems coupled to the optical network; a fabric coupled to the one ormore optical modems for switching of connections; and a processingdevice implementing a control agent, wherein the control agent isconfigured to determine that a modulation change is warranted for anoptical modem in the node, the optical modem is configured tocommunicate over an optical link, determine an impact of the modulationchange on the optical link and associated underlying connectionsthereon, cause changes in a data plane for the associated underlyingconnections through the fabric, prior to performing the modulationchange, and cause the modulation change subsequent to accommodating theassociated underlying connections in the data plane, thereby minimizinginterruptions of the associated underlying connections due to themodulation change. The changes can be caused in the data plane utilizinga control plane and restoration of the associated underlying connectionsper normal control plane behavior with the fabric.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings, in which like reference numbers areused to denote like system components/method steps, as appropriate, andin which:

FIG. 1 is a network diagram of an exemplary network for the systems andmethods for managing excess optical capacity and margin in opticalnetworks;

FIG. 2 are graphs of an example of spectral shaping fitting a 100Gsignal into 50 GHz of bandwidth and into 25 GHz of bandwidth or less;

FIG. 3 is a flowchart of a method for managing excess optical capacityand margin in optical networks;

FIG. 4 is a flowchart of another method for managing excess opticalcapacity and margin in optical networks;

FIG. 5 is a flowchart of a coexistence method for managing excessoptical capacity and margin in optical networks with both variablecapacity channels and fixed capacity channels intermixed;

FIG. 6 is a block diagram of an exemplary network element for use withthe methods and systems described herein;

FIG. 7 is a block diagram of a controller to provide control planeprocessing and/or operations, administration, maintenance, andprovisioning (OAM&P) for the network element of FIG. 6;

FIG. 8 is a block diagram of a hitless modulation change system at anode connected to an optical network; and

FIG. 9 is a flow chart of a hitless modulation change method which canbe implemented through the control agent in coordination with the modem,the control plane, etc. from the hitless modulation change system ofFIG. 8; and

FIG. 10 is a block diagram of a processing device that can operate thecontrol agent from the hitless modulation change system of FIG. 8.

DETAILED DESCRIPTION OF THE DISCLOSURE

In various exemplary embodiments, hitless modulation scheme changesystems and methods in optical networks are described. The hitlessmodulation scheme change systems and methods allow modulation schemechanges of a transponder in a hitless manner so as to reap the benefitof changing the spectral efficiency to match link and system levelrequirements. The hitless modulation scheme change systems and methodsprovide a bottom-up approach and autonomous approach that negotiates amodulation change when one is warranted and ensures that existingtraffic is not impacted during the modulation change. Due to the complexnature of high-speed optical transmission (e.g., coherent modulation,adaptive electrical signal processing, Forward Error Correction (FEC),etc.), it is extremely complex to switch a transponder or modem'smodulation without impacting traffic. In this manner, the hitlessmodulation scheme change systems and methods propose an approach using amechanism which coordinates between a data plane and control plane, i.e.using a fabric and a modem, to ensure current traffic is minimallyimpacted from a modulation scheme change. Note, as described herein, ahitless change means one in which traffic is impacted by 50 ms or lessor by an amount based on service restoration (e.g., a mesh restorationevent may be more than 50 ms). On the contrary, a modulation schemechange can take on the order of seconds to implement, given currentimplementations. It is expected that this amount of time will decrease,such as to 1 s or less, but still higher than 50 ms.

Additionally, in various exemplary embodiments, systems and methods formanaging excess optical capacity and margin in optical networks aredescribed. Fundamentally, the systems and methods exploit the fact thatnext-gen flexible optical modems can support various bit-rates wellbeyond a guaranteed bit-rate in most operating situations (i.e., theguaranteed bit-rate is engineered for full-fill or worst-case, and inall other situations, higher bit-rates typically can be achieved). Inthe systems and methods described herein, techniques are described toactively mine this excess capacity to provide additional bandwidthwithout additional hardware that can be used for various purposes suchas restoration traffic, short-lived bandwidth-on-demand connections, orthe like. In an exemplary aspect, the systems and methods describedherein are advantageous in first-in builds in that this excess capacitycan be used for restoration traffic without requiring additionalhardware in low-fill deployments. This can significantly lower the costsof first-in builds. Further, the systems and methods described hereincontemplate integration between the flexible optical modems; amanagement system, management plane, and/or control plane; a switchingplane to enable use and management of this excess capacity as one ormore logical interfaces.

Exemplary Network

Referring to FIG. 1, in an exemplary embodiment, a network diagramillustrates an exemplary network 10 implementing the systems and methodsfor managing excess optical capacity and margin in optical networks. Thenetwork 10 includes two interconnected network elements 12 a, 12 b viaan optical link 14. Additionally, the optical link 14 can includeadditional components 16 which are omitted for illustration purposes.For example, the additional components 16 can include, withoutlimitation, optical amplifiers, optical add/drop multiplexers (OADMs),reconfigurable OADMs (ROADMs), etc. In the context of the systems andmethods, the network elements 12 a, 12 b are connected via the opticallink 14 which is all-optical between the network elements 12 a, 12 b,i.e. no optical-electrical-optical (OEO) conversions between the networkelements 12 a, 12 b. The optical link 14 can be a single span ormultiple spans with intermediate amplifiers. Those of ordinary skill inthe art will recognize that the network 10 can include other networkelements 12 a, 12 b forming various architectures, i.e. mesh, rings,linear, etc. The network 10 is presented as a single optical link(optionally with the components 16) for an illustration of the systemsand methods.

The optical link 14 can include N channels (or wavelengths), denoted asλ₁-λ_(n). For example, the number N can be the maximum supportedchannels on the optical link 14. Additionally, the number N can bevariable with respect to flexible grid channels (e.g., channels takingan arbitrary and variable amount of spectrum). For example, N can be 44for 100 GHz channel spacing, 88 for 50 GHz channel spacing, or anycombination in between to deliver between 36 and 88 wavelengths withflexible grid channels. Other embodiments are also contemplated. From alink engineering perspective, the optical link 14 is designed andimplemented day one to support the N channels. However, greenfieldinstallation or first-in builds (i.e., new) typically only include oneor a couple of channels. Also, it can often take time to move from thecouple of channels to a full complement of the N channels on the opticallink 14. This can be referred to as a forecast tolerant modeling schemewhere the optical link 14 is designed to support a full-fill that willeventually be realized, but is likely not present in first-in builds.Thus, from a system capacity perspective, the optical link 14 hasunutilized margin and capacity in the first-in builds and where theoptical link 14 has less than N channels deployed thereon.

In the context of the N channels, the N channels are either fixedcapacity channels or variable capacity channels depending on associatedhardware at the network elements 12 a, 12 b forming each of the Nchannels. In an exemplary embodiment, the optical line 14 can includeone or more fixed capacity channels, one or more variable capacitychannels, and/or a combination thereof. Fixed capacity channels areimplemented through optical transceivers, transponders, muxponders(i.e., M:N combiners), etc. Here, the fixed capacity channels do nothave an ability to vary the bandwidth, i.e. a 10 Gbps transponder withfixed capacity can only support 10 Gbps worth of traffic, etc. Fixedcapacity channels may also include fixed channel spacing (e.g., 50/100GHz) (i.e., fixed grid channels) and fixed FEC overhead. For a fixedcapacity channel, if a channel has X dB excess margin, there is no waythe fixed capacity channel can make use of this excess margin, i.e. thefixed capacity channel hardware is not configured to vary the bandwidth.

Variable capacity channels are implemented through flexible opticalmodems. In contrast to the fixed capacity channels, variable capacitychannels typically include adaptable coherent modulation or non-coherentmodulation, adaptive FEC schemes, and spectral shaping. A flexibleoptical modem can support a variable amount of bandwidth, e.g. from xGbps to y Gbps, where x<y. For example, a flexible optical modem cansupport a guaranteed rate, e.g. 40G, 100G, 400G, 1T, etc. along with ahigher supported rate, e.g. 40G->100G, 100G->200G, 400G->1T, etc. Theflexible optical modem utilizes the adaptable coherent modulation,adaptive FEC schemes, and spectral shaping to support the variableamount of bandwidth. The limitations on the upper bound of the variableamount of bandwidth are based on i) what the optical link 14 cansupport, ii) backplane interfaces in the network element 12 a, 12 b withthe flexible optical modem, and iii) adaptive modulation formatssupported. An example of a flexible optical modem is the WaveLogic 3from Ciena Corporation, the assignee of the present application/patent.Also, note the flexible optical modem may also be referred to as atransceiver, transponder, muxponder, etc.

With respect to adaptive coherent modulation, the flexible optical modemcan support various different baud rates through software-programmablemodulation formats. The flexible optical modem can support programmablemodulation, or constellations with both varying phase and/or amplitude.In an exemplary embodiment, the flexible optical modem can supportmultiple coherent modulation formats such as, for example, i)dual-channel, dual-polarization (DP) binary phase-shift keying (BPSK)for 100G at submarine distances, ii) DP quadrature phase-shift keying(QPSK) for 100G at ultra long haul distances, iii) 16-quadratureamplitude modulation (QAM) for 200G at metro to regional (600 km)distances), or iv) dual-channel 16QAM for 400G at metro to regionaldistances. Thus, in this exemplary embodiment, the same flexible opticalmodem hardware can support 100G to 400G. With associated digital signalprocessing (DSP) in the flexible optical modem hardware, moving from onemodulation format to another is completely software-programmable. Inanother exemplary embodiment, the flexible optical modem can supportN-QAM modulation formats with and without dual-channel anddual-polarization where N can even be a real number and not necessarilyan integer. Here, the flexible optical modem can support non-standardspeeds since N can be a real number as opposed to an integer, i.e. notjust 100G, 200G, or 400G, but variable speeds, such as 130G, 270G, 560G,etc. Furthermore, with the DSP and software programming, the capacity ofthe flexible optical modem can be adjusted upwards or downwards in ahitless manner so as to not affect the guaranteed rate.

With respect to the adaptive FEC schemes, the flexible optical modem cansupport a new soft-decision forward error correction (soft FEC)algorithm. The soft FEC can be software-programmable to adjust for lowlatency demands versus capacity/performance demands. The soft FEC usesvariable-rate FEC codes which can take up variable amounts of an overallsignal, e.g. 20%, 16%, 10%, 7%, etc. As is known in the art, thestronger the FEC, the more margin in dB is provided. In this manner, thesoft FEC provides another opportunity to mine the excess capacity on avariable capacity channel. For example, assume a variable capacitychannel is deployed with 20% FEC overhead with margin of 10 dB. The FECcan be reduced, e.g., to 10% to reduce the margin and provide excesscapacity for use. The strong FEC may not be needed until more channelsare added to the optical link 14. An example of a soft-decision forwarderror correction algorithm is described in Gho et al., “Rate-AdaptiveCoding for Optical Fiber Transmission Systems,” IEEE JOURNAL OFLIGHTWAVE TECHNOLOGY, VOL. 29, NO. 2, Jan. 15, 2011, the contents ofwhich are incorporated by reference herein. Note, the fixed capacitychannel hardware may also implement FEC as well as a soft FEC. However,as described herein, the fixed capacity channel hardware isdistinguishable from the variable capacity channel hardware in that itdoes not support an ability to mine the excess capacity. Rather, thefixed capacity channel hardware only supports a single guaranteed rate.

With respect to spectral shaping, the flexible optical modems canoperate in both fixed- and flexible-grid environments. Referring to FIG.2, in an exemplary embodiment, a spectral diagram illustrates an exampleof fitting a 100G signal into 50 GHz of bandwidth (graph 20 representinga QPSK 100G signal), into 25 GHz of bandwidth (graph 22 representing a16QAM 100G signal), and into less than 25 GHz of bandwidth (graph 22 arepresenting a spectrally shaped 16QAM 100G signal). Note, the 16QAM100G which uses half the baud rate of the QPSK 100G. If one is on afixed grid, there is no gain in spectral efficiency, e.g. both signalsfit into a 50 GHz channel. If one is allowed to change the channelspacing flexibly, then the spectral efficiency can be doubled, e.g. two16QAM 100G signals in 50 GHz spacing. For example, in a first-in buildsolely with flexible optical modems, it may be advantageous to use aflexible-grid and space each 100G signal in the minimal amount ofbandwidth. However, in an existing fixed-grid, it may be required to fitthe 100G into 50 GHz of bandwidth. Here, in an exemplary embodiment, thesystems and methods propose to intentionally harm fixed capacitychannels with excess, but unusable margin to allow the flexible opticalmodem to use the excess margin.

Variously, it is an exemplary objective of the systems and methods tomine this unutilized margin and capacity to lower first-in network costby allowing network operators to defer deploying excess capacity.Specifically, through the flexible optical modems, the systems andmethods leverage the ability of the lines to provide the restorationbandwidth thereby deferring the deployment of additional opticalinterfaces as well as provide excess capacity that can be utilized forlower priority services, bandwidth-on-demand, etc. Specifically,first-in builds have significant excess margin, and with the emergenceof flexible optical modems, it is an objective to provide and manage theexcess margin to provide excess capacity without additional hardware ormanagement constraints. That is, the flexible optical modems cansignificantly reduce initial costs by providing extra capacity that canbe used for restoration, short-lived on-demand connections, or excesscapacity with lower service-level agreements (SLAs). In conjunction withthe foregoing, the systems and methods also include integration of thisextra capacity with a management system, management plane, and/orcontrol plane in the network 10 or other networks.

Managing Excess Optical Capacity and Margin

Referring to FIG. 3, in an exemplary embodiment, a flowchart illustratesa method 100 for managing excess optical capacity and margin in opticalnetworks. The method 100 contemplates operation in the network 10 andother optical networks including flexible optical modems for variablecapacity channels (and optionally with fixed capacity channels presentas well.) The method 100 can be implemented on a single channel orwavelength of a flexible optical modem. The method 100 can beimplemented on multiple channels concurrently or in series. For example,in series, each iteration of the method 100 may affect each subsequentiteration as the increased bandwidth of one channel may reduce theexcess margin of the next. Performed concurrently, the method 100 may bebased on a local determination of excess margin at each flexible opticalmodem without regard for collocated channels. The concurrent methodcould be independent (as stated) or in concert. Independent meaning thatit is done per-channel without regard for other collocated channels, andin concert meaning that the margin of each channel is calculated takinginto account the effect of the other collocated channels. This requiresa “master” or nodal controller to amalgamate the channel information andperform the calculation.

The method 100 includes determining excess margin relative to a nominalguaranteed rate of a flexible optical modem (step 102). The nominalguaranteed rate can be the rate at which the flexible optical modem isconfigured to operate with a full-fill on the associated optical line.Also, the nominal guaranteed rate can be the rate that is guaranteedthrough link engineering to work under any conceivable condition on theoptical line such as full-fill. The excess margin (in dB) is the extramargin that the flexible optical modem presently sees given the currentconditions on the optical line (e.g., channel count). That is, theexcess margin is determined relative to margin needed to ensureperformance at a nominal guaranteed rate. As stated herein, it isexpected that on first-in deployments, the flexible optical modem maysee significant margin given the engineering requirement to design forworst case (i.e., full-fill).

With the determined excess margin, the method 100 includes increasingcapacity of the flexible optical modem to consume most or all of theexcess margin (step 104). Thus, the flexible optical modem supports anominal guaranteed rate for guaranteed bandwidth and an excess rate forexcess bandwidth where the excess rate minus the nominal guaranteed rateequals the excess capacity. Here, the method 100 can use all of theexcess margin or most of it, leaving a small amount (e.g., 1 dB or less)for cushion to ensure the nominal guaranteed rate.

Next, the method 100 includes mapping the excess capacity to one or morelogical interfaces (step 106). The logical interfaces are typically 1:1mapped with physical interfaces. Specifically, the logical interfacesare used by a management system, management plane, and/or control planeto map physical interfaces onto the optical line. Exemplary logicalinterfaces can be defined in terms of bandwidth such as, for example,155 Mpbs (Synchronous Transport Signal-level 1 (STS-1) or VC3), N×155Mpbs (N×STS-1), 1 Gbps (GbE), 2.5 Gbps (OC-48/STM-1, OTU1, ODU1), 10Gbps (OC-192/STM-64, OTU2, ODU2, 10 GbE), 40 Gbps (OC-768/STM-256, OTU3,ODU3, 40 GbE), 100 Gbs (OTU4, ODU4, 100 GbE), variable capacity ODUFlex,and the like. The logical interfaces can also be defined by signal typesuch as, for example, sub-network connections (SNCs), label switchedpaths (LSPs), 2F/4F BLSRs, 1+1/1:1 APS lines, UPSRs, VPSRs, 0:1unprotected lines, etc. That is, the logical interfaces representanything that allows the management system, management plane, and/orcontrol plane to utilize the physical excess capacity from the method100 in a network along with various switches.

The management system, management plane, and/or control plane areconfigured to recognize the excess capacity is terms of the associatedlogical interfaces and to allow physical hardware at the networkelements 12 to support these extra logical interfaces. From a hardwareperspective, the extra logical interfaces are formed on the optical linevia the flexible optical modems in accordance with the method 100. Atthe network elements 12 or collocated therewith, switches can beconfigured to process the extra logical interfaces through associatedswitching fabrics. Again, the management system, management plane,and/or control plane recognize these additional logical interfaces asextra traffic without requiring additional hardware (assuming theswitching fabrics can support the additional capacity). Note, FIGS. 6-7illustrate an exemplary network element 12 and associated control modulefor use with the systems and methods described herein.

In an exemplary embodiment, the method 100 includes flagging thebandwidth created in the step 106 on the one or more logical interfacesas excess capacity. For example, the flagging can include notifying themanagement system, management plane, and/or control plane that the oneor more logical interfaces are excess capacity. The reason is to flag tothe management system, management plane, and/or control plane is thatthis capacity can disappear and this needs to be accounted for. Themethod 100 can be periodically reiterated for each flexible opticalmodem. For example, the method 100 can be reiterated at set intervals orbased on an occurrence such as channel additions/deletions on theoptical lines or margin changes/erosion on the optical lines. With eachiteration of the method 100, it is possible that the one or more logicalinterfaces could disappear or increase. For example, if channels areadded to a line and the method 100 is rerun, the excess capacity couldbe decreased since the additional channels will likely reduce the excessmargin. With a reduction in the excess capacity, some or all of thelogical interfaces based thereon could disappear as the flexible opticalmodem scales back bandwidth or returns to the nominal guaranteed rate.

Accordingly, in an exemplary aspect, the method 100 contemplates usingthese logical interfaces based on the excess capacity for restorationbandwidth in new or low-fill optical networks as well as forbandwidth-on-demand, i.e. short-lived SNCs or LSPs, etc., and lower costbandwidth with minimal SLA requirements. Specifically, in first-inbuilds, the method 100 can significantly reduce costs using the logicalinterfaces based on the excess capacity as mesh restoration SNCs orLSPs. This can defer the cost of additional optical interfaces to formunused capacity that is dedicated for restoration. Thus, in first-inbuilds, all optical hardware can be utilized for revenue generation.

Referring to FIG. 4, in an exemplary embodiment, a flow chartillustrates another method 200 for managing excess optical capacity andmargin in optical networks. The method 200 is similar to the method 100and provides additional details. Similarly, the method 200 contemplatesoperation in the network 10 and other optical networks, includingflexible optical modems for variable capacity channels (and optionallywith fixed capacity channels present as well.) The method 200 can beimplemented on a single channel or wavelength of a flexible opticalmodem. The method 200 can be implemented on multiple channelsconcurrently or in series. For example, in series, each iteration of themethod 200 may affect each subsequent iteration as the increasedbandwidth of one channel may reduce the excess margin of the next.Performed concurrently, the method 200 may be based on a localdetermination of excess margin at each flexible optical modem withoutregard for collocated channels. The concurrent method could beindependent (as stated) or in concert. Independent meaning that it isdone per-channel without regard for other collocated channels, and inconcert meaning that the margin of each channel is calculated takinginto account the effect of the other collocated channels. This requiresa “master” or nodal controller to amalgamate the channel information andperform the calculation.

The method 200 includes computing or providing a route for a networkdemand (step 202). The network demand is a guaranteed amount ofbandwidth needed in the network between two optical network elements 12,e.g. 10G, 40G, 100G, etc. The method 200 can receive an explicit routeor calculate a route using control plane techniques. Next, the method200 includes determining path viability for the route and the networkdemand for an ideal bit-rate using a forecast tolerant modeling scheme(step 204). For example, this functionality can be performed in amanagement system, an optical modeling system, etc., and thisfunctionality includes determining the guaranteed wavelength capacityunder worst-case conditions such as at full-fill, etc. That is, theforecast tolerant modeling scheme ensures the network demand can beserviced by the route regardless of future constraints. The step 204could also optionally include a wavelength assignment. The selection ofwavelength could take into account the selection of wavelengthscurrently available (not in use).

Next, the method 200 includes determining path viability for the routeand a maximum supported capacity on the existing network (step 206). Thestep 206 could also optionally include a wavelength assignment. Theselection of wavelength in this case could differ from the step 204 inthat it could select wavelengths which maximize the potential excessbandwidth. For example, it could choose to separate wavelengths fromthose already in service or to allocate a different spectral width tothe channel being routed. The wavelength assignment in this step couldchange the wavelength previously chosen in step 204. Alternatively, thisexcess bandwidth aware wavelength assignment could be applied in step204.

The step 204 looks at the worst case, whereas the step 206 looks atcurrent conditions (i.e., right now without adding in margin for addedchannels or end-of-life operation). The step 204 determines theguaranteed wavelength capacity while the step 206 determines the currentmaximum wavelength capacity. It is the delta between these two scenariosthat constitutes the excess margin and capacity opportunities withflexible optical modems. From a computation perspective, assign thevalue determined in the step 206 as Max and:Max_Engineered=Max−δ_(margin)where Max_Engineered is the maximum currently supported bandwidth, Maxis the result of the step 206 (i.e., the physical maximum bandwidth),and δ_(margin) is a small engineering margin simply to avoid a signaldegrade threshold and this value can be 0 or a small amount such as <1dB. The result of the step 204 can be denoted as Guaranteed, i.e. theguaranteed wavelength capacity. Accordingly:Excess=Max_Engineered−Guaranteedwhere Excess is the additional excess capacity currently supported thatcan be mined by the method 200 (or the method 100).

Next, the method 200 includes installing and/or activating a wavelengthin the network at the Max_Engineered rate with a logical interfacethereon supporting the guaranteed rate for the network demand and one ormore logical interfaces providing the excess capacity (step 208). Here,the method 200, similar to the method 100, can provide these one or morelogical interfaces from the excess capacity to a management plane and aswitching plane for use thereof as restoration capacity,bandwidth-on-demand (BOD), short-lived services, etc. The method 200 canimplement the various functionality described in the method 100 as wellfor implementing the one or more logical interfaces from the excesscapacity.

The method 200 will operate with the logical interface supporting theguaranteed rate and with the one or more logical interfaces providingthe excess capacity until a margin erosion, signal degradation, or otherchange (step 210). Again, it is expected at the client layer that thelogical interface for the guaranteed capacity can be used for anyservice request, but specifically long lived traffic. On the other hand,the client layer could use the excess capacity for any service request,but it would be prudent to only use it for temporary traffic (e.g.restoration traffic, bandwidth-on-demand with a known termination dateand time, etc.). In the method 200, if there is margin erosion or asignal degrade crossing (step 210), the flexible optical modem can dropthe excess capacity and hitlessly revert back to the guaranteed bit-rate(step 212). In this way, the excess margin is now used to make up forthe margin erosion or the signal degrade crossing and not for the excesscapacity. The excess capacity is lost, but the guaranteed capacity isprotected from the margin erosion or the signal degrade crossing.

Once stability has been achieved for a set amount of time (e.g., 5minutes, 2 hours, etc.) (step 214), the method 200 can includeperforming path viability for the route and a maximum supported capacityon the existing network (step 216). The step 216 is similar to the step206. Once it is determined what excess margin exists after stability,the flexible optical modem can hitlessly increase its rate based on themaximum supported rate from the step 216 (and the guaranteed rate fromthe step 204). Also, if a path completely fails, then an alternate pathis computed (per typical control plane behavior) and installed. Themethod 200 can operate as well on the new alternate path. For example,the method 200 can be implemented subsequent to a protection switchafter stability is achieved.

Referring to FIG. 5, in an exemplary embodiment, a flow chartillustrates a coexistence method 300 for managing excess opticalcapacity and margin in optical networks with both variable capacitychannels and fixed capacity channels intermixed. Specifically, thecoexistence method 300 contemplates operation along with the methods100, 200 in the network 10 and other optical networks, includingflexible optical modems for variable capacity channels and with fixedcapacity channels present as well. The coexistence method 300 beginswith an assumption that any excess margin on a fixed capacity channel isunusable as discussed herein. The coexistence method 300 looks foropportunities to reduce this unusable excess margin to increase theexcess margin on variable capacity channels for increased excesscapacity according to the methods 100, 200.

The method 300 includes one or more variable capacity channels operatingor planned on being operated on a same optical line or link as one ormore fixed capacity channels (step 302). The method 300 can beimplemented at various stages—in new systems where just a couple ofchannels are used all the way up to full-fill. The method 300 checks ifthere is an excess margin for any of the fixed capacity channels (step304), and if not, the method 300 ends (step 306). If there is an excessmargin on any of the fixed capacity channels (step 304), the method 300utilizes various techniques to mine this excess margin for the benefitof the variable capacity channels (which in turn can implement themethods 100, 200 whereas the fixed capacity channels cannot).

The method 300 can include positioning or ensuring the variable capacitychannels are located adjacent to fixed capacity channels on the opticalspectrum (step 308). That is, it is advantageous for the method 300 tohave fixed capacity channels adjacent to the variable capacity channelsas opposed to separating these channels on the spectrum. The method 300includes intentionally increasing performance of the variable capacitychannels at the expense of the fixed capacity channels (with excessmargin) to reduce the excess margin for the fixed capacity channelswhile concurrently increasing the excess margin for the variablecapacity channel (step 310). In a way, it can be said that the method300 intentionally harms the fixed capacity channels to remove the excessmargin so it can be used by the variable capacity channels.

The method 300 contemplates various options for adjusting both the fixedcapacity channels with excess margin and the variable capacity channels.For example, the fixed capacity channels could be transmitted at loweroutput powers to make these channels less intrusive to neighboringvariable capacity channels and therefore increase performance of theneighboring variable capacity channels. Further, the fixed capacitychannels could be transmitted at a reduced baud rate and increasedsignal density to transmit in a format that takes more OSNR but usesless spectrum. Also, the variable capacity channel can intrude into thespectrum of the fixed capacity channel. For example, in FIG. 2, thevariable capacity channel can extend 10 GHz into each of its neighborsto support 70 GHz of bandwidth versus 50 GHz thereby providing anadditional margin for the variable capacity channel.

The method 300 can install or increase bit-rate of the variable capacitychannels based on the increased performance and margin “stolen” from thefixed capacity channels and map this excess capacity to one or morelogical interfaces such as described in the methods 100, 200 (step 312).In an exemplary embodiment, a method includes determining excess marginrelative to margin needed to insure performance at a nominal guaranteedrate associated with a flexible optical modem configured to communicateover an optical link; causing the flexible optical modem to consume mostor all of the excess margin, wherein the capacity increased above thenominal guaranteed rate includes excess capacity; and mapping the excesscapacity to one or more logical interfaces for use by a managementsystem, management plane, and/or control plane. The method can furtherinclude utilizing the one or more logical interfaces by the managementsystem, management plane, and/or control plane as one of restorationbandwidth or short-lived bandwidth-on-demand connections. The method canfurther include determining the excess margin relative to the nominalguaranteed rate through the steps of: determining path viability of anetwork demand over the optical link for an ideal bit-rate using aforecast tolerant modeling scheme; determining path viability for amaximum supported capacity over the optical link based on existingconditions on the optical link; and determining the excess margin as adifference between the path viability for a maximum supported capacityand the path viability of the network demand along with including asmall engineering margin. The method can further include detectingmargin erosion or a signal degrade on the flexible optical modem; anddropping the excess capacity and hitlessly reverting to the nominalguaranteed rate. The method can further include after a period ofstability subsequent to the margin erosion or the signal degrade,determining again the path viability for a new maximum supportedcapacity over the optical link based on existing conditions on theoptical link; and hitlessly increasing a rate of the flexible opticalmodem based on the new maximum supported capacity.

The method can further include updating the determined excess marginrelative to the nominal guaranteed rate in the flexible optical modemresponsive to channels added or deleted on the optical link. Theflexible optical modem can form a variable capacity channel, wherein theoptical link can include a fixed capacity channel adjacent to thevariable capacity channel, and the method can further includedetermining excess margin for the fixed capacity channel that isunusable since the fixed capacity channel cannot modify its rate;increasing performance of the variable capacity channel and/ordecreasing performance of the fixed capacity channel based on the excessmargin for the fixed capacity channel; and increasing bit-rate of thevariable capacity channel based on margin gained by the increasedperformance of the variable capacity channel and/or the decreasedperformance of the fixed capacity channel. The method can furtherinclude increasing performance of the variable capacity channelincluding extending associated optical spectrum into optical spectrumfrom the fixed capacity channel; and decreasing performance of the fixedcapacity channel includes any of lowering output power to make the fixedcapacity channel less intrusive to the variable capacity channel, ortransmitting at a reduced baud rate and/or increased signal density totransmit in a format that uses less of the optical spectrum. The methodcan further include operating a control plane; and utilizing the one ormore logical interfaces for restoration sub-network connections or labelswitched paths.

In another exemplary embodiment, a network element includes at least oneflexible optical modem; and a controller configured to: determine excessmargin relative to margin needed to insure performance at a nominalguaranteed rate associated with the at least one flexible optical modemconfigured to communicate over an optical link; cause the at least oneflexible optical modem to consume most or all of the excess margin,wherein the capacity increased above the nominal guaranteed rateincludes excess capacity; and map the excess capacity to one or morelogical interfaces for use by a management system, management plane,and/or control plane. The controller can be further configured toutilize the one or more logical interfaces as one of restorationbandwidth or short-lived bandwidth-on-demand connections. The controllercan be further configured to determine the excess margin relative to thenominal guaranteed rate through the steps of: determine path viabilityof a network demand over the optical link for an ideal bit-rate using aforecast tolerant modeling scheme; determine path viability for amaximum supported capacity over the optical link based on existingconditions on the optical link; and determine the excess margin as adifference between the path viability for a maximum supported capacityand the path viability of the network demand along with including asmall engineering margin. The controller can be further configured todetect margin erosion or a signal degrade on the at least one flexibleoptical modem; and drop the excess capacity and hitlessly reverting tothe nominal guaranteed rate.

The controller can be further configured to, after a period of stabilitysubsequent to the margin erosion or the signal degrade, determine againthe path viability for a new maximum supported capacity over the opticallink based on existing conditions on the optical link; and hitlesslyincrease a rate of the flexible optical modem based on the new maximumsupported capacity. The controller can be further configured to updatethe determined excess margin relative to the nominal guaranteed rate inthe at least flexible optical modem responsive to channels added ordeleted on the optical link. The at least one flexible optical modem canform a variable capacity channel, wherein the optical link includes afixed capacity channel adjacent to the variable capacity channel, andthe controller can be further configured to determine excess margin forthe fixed capacity channel that is unusable since the fixed capacitychannel cannot modify its rate; increase performance of the variablecapacity channel and/or decreasing performance of the fixed capacitychannel based on the excess margin for the fixed capacity channel; andincrease a bit-rate of the variable capacity channel based on margingained by the increase performance of the variable capacity channeland/or the decreased performance of the fixed capacity channel. Thecontroller can be further configured to increase performance of thevariable capacity channel including extending associated opticalspectrum into optical spectrum from the fixed capacity channel; anddecrease performance of the fixed capacity channel including the oflowering output power to make the fixed capacity channel less intrusiveto the variable capacity channel, or transmitting at a reduced baud rateand/or increased signal density to transmit in a format that uses lessof the optical spectrum. The controller can be further configured tooperate a control plane; and utilize the one or more logical interfacesfor restoration of sub-network connections or label switched paths.

In yet another exemplary embodiment, a network includes a plurality ofinterconnected network elements, at least one link in the network formedbetween two of the plurality of interconnected network elements isformed by flexible optical modems; a control plane communicativelycoupled to the plurality of interconnected network elements; and acontroller communicatively coupled to the flexible optical modems andconfigured to: determine excess margin needed to insure performance at anominal guaranteed rate over the at least one link; cause the flexibleoptical modems to consume most or all of the excess margin, wherein thecapacity increased above the nominal guaranteed rate includes excesscapacity; and map the excess capacity to one or more logical interfacesfor use by the control plane. The controller can be further configuredto utilize the one or more logical interfaces as one of restorationbandwidth or short-lived bandwidth-on-demand connections.

Exemplary Network Element

Referring to FIG. 6, in an exemplary embodiment, a block diagramillustrates an exemplary network element 12 for use with the methods andsystems described herein. In an exemplary embodiment, the exemplarynetwork element 12 can be a network element that may consolidate thefunctionality of a multi-service provisioning platform (MSPP), digitalcross connect (DCS), Ethernet and/or Optical Transport Network (OTN)switch, dense wave division multiplexed (DWDM) platform, etc. into asingle, high-capacity intelligent switching system providing Layer 0, 1,and 2 consolidation. In another exemplary embodiment, the networkelement 12 can be any of an OTN add/drop multiplexer (ADM), aSONET/SDH/OTN ADM, a multi-service provisioning platform (MSPP), adigital cross-connect (DCS), an optical cross-connect, an opticalswitch, a router, a switch, a wavelength division multiplexing (WDM)terminal, an access/aggregation device, etc. That is, the networkelement 12 can be any digital system with ingress and egress digitalsignals and switching therebetween of channels, timeslots, tributaryunits, wavelengths, etc. utilizing OTN, SONET, SDH, etc. Alternatively,the network element 12 can exclude digital switching and solely provideoptical switching and/or transmission. While the network element 12 isgenerally shown as an optical network element, the systems and methodscontemplated for use with any switching fabric, network element, ornetwork based thereon.

In an exemplary embodiment, the network element 12 includes commonequipment 410, one or more line modules 420, and one or more switchmodules 430. The common equipment 410 can include power; a controlmodule; operations, administration, maintenance, and provisioning(OAM&P) access; user interface ports; and the like. The common equipment410 can connect to a management system 450 through a data communicationnetwork 460. The management system 450 can include a network managementsystem (NMS), element management system (EMS), or the like.Additionally, the common equipment 410 can include a control planeprocessor configured to operate a control plane as described herein. Thenetwork element 12 can include an interface 470 for communicativelycoupling the common equipment 410, the line modules 420, and the switchmodules 430 therebetween. For example, the interface 470 can be abackplane, mid-plane, a bus, optical or electrical connectors, or thelike. The line modules 420 are configured to provide ingress and egressto the switch modules 430 and external to the network element 12. In anexemplary embodiment, the line modules 420 can form ingress and egressswitches with the switch modules 430 as center stage switches for athree-stage switch, e.g. a three stage Clos switch. Other configurationsand/or architectures are also contemplated. The line modules 420 caninclude optical transceivers, such as, for example, 1 Gbps (GbE PHY),2.5 Gbps (OC-48/STM-1, OTU1, ODU1), 10 Gbps (OC-192/STM-64, OTU2, ODU2,10 GbE PHY), 40 Gbps (OC-768/STM-256, OTU3, ODU3, 40 GbE PHY), 100 Gbps(OTU4, ODU4, 100 GbE PHY), etc.

Further, the line modules 420 can include a plurality of opticalconnections per module and each module may include a flexible ratesupport for any type of connection, such as, for example, 155 Mbps, 622Mbps, 1 Gbps, 2.5 Gbps, 10 Gbps, 40 Gbps, 100 Gbps, 400 Gbps, 1 Tbps,and any rate in between. The line modules 420 can include wavelengthdivision multiplexing interfaces, short reach interfaces, and the like,and can connect to other line modules 420 on remote network elements,end clients, edge routers, and the like. From a logical perspective, theline modules 420 provide ingress and egress ports to the network element12, and each line module 420 can include one or more physical ports. Asdescribed herein the line modules 420 can support either fixed capacitychannels or variable capacity channels. The line modules 420 can betransponders, muxponders, flexible optical modems, etc. Note, if thenetwork element 12 is a DWDM terminal, the switch modules 430 may beomitted and the line modules 420 act as transponders, muxponders, etc.It is assumed that a switch device is at some point connected to theDWDM terminal to support the one or more logical interfaces that areformed from the excess capacity.

The switch modules 430 are configured to switch channels, timeslots,tributary units, etc. between the line modules 420. For example, theswitch modules 430 can provide wavelength granularity (Layer 0switching), SONET/SDH granularity such as Synchronous Transport Signal-1(STS-1) and variants/concatenations thereof (STS-n/STS-nc), SynchronousTransport Module level 1 (STM-1) and variants/concatenations thereof,Virtual Container 3 (VC3), etc.; OTN granularity such as Optical ChannelData Unit-1 (ODU1), Optical Channel Data Unit-2 (ODU2), Optical ChannelData Unit-3 (ODU3), Optical Channel Data Unit-4 (ODU4), Optical ChannelData Unit-flex (ODUflex), Optical channel Payload Virtual Containers(OPVCs), ODTUGs, etc.; Ethernet packet granularity; Digital Signal n(DSn) granularity such as DS0, DS1, DS3, etc.; and the like.Specifically, the switch modules 630 can include both Time DivisionMultiplexed (TDM) (i.e., circuit switching) and packet switchingengines. The switch modules 430 can include redundancy as well, such as1:1, 1:N, etc. In an exemplary embodiment, the switch modules 430provide OTN, SONET, or SDH switching.

Those of ordinary skill in the art will recognize the network element 12can include other components which are omitted for illustrationpurposes, and that the systems and methods described herein arecontemplated for use with a plurality of different network elements withthe network element 12 presented as an exemplary type of networkelement. For example, in another exemplary embodiment, the networkelement 12 may not include the switch modules 430, but rather have thecorresponding functionality in the line modules 420 (or some equivalent)in a distributed fashion or completely omit the correspondingfunctionality as in the case of a DWDM terminal. For the network element12, other architectures providing ingress, egress, and switchingtherebetween are also contemplated for the systems and methods describedherein. In general, the systems and methods described herein contemplateuse with any network element providing switching and/or transport ofOTN, SONET, SDH, etc. channels, timeslots, tributary units, wavelengths,packets, etc. Furthermore, the network element 12 is merely presented asone exemplary implementation for the systems and methods describedherein. Those of ordinary skill in the art will recognize the systemsand methods can be used for practically any type of network element thatincludes flexible optical modems for supporting variable capacitychannels.

Exemplary Controller

Referring to FIG. 7, in an exemplary embodiment, a block diagramillustrates a controller 500 to provide control plane processing and/oroperations, administration, maintenance, and provisioning (OAM&P) forthe network element 12. The controller 500 can be part of commonequipment, such as common equipment 410 in the network element 12. Thecontroller 500 can include a processor 502 which is hardware device forexecuting software instructions such as operating the control plane. Theprocessor 502 can be any custom made or commercially availableprocessor, a central processing unit (CPU), an auxiliary processor amongseveral processors associated with the controller 500, asemiconductor-based microprocessor (in the form of a microchip or chipset), or generally any device for executing software instructions. Whenthe controller 500 is in operation, the processor 502 is configured toexecute software stored within memory, to communicate data to and fromthe memory, and to generally control operations of the controller 500pursuant to the software instructions. The controller 500 can alsoinclude a network interface 504, a data store 506, memory 508, an I/Ointerface 510, and the like, all of which are communicatively coupledtherebetween and with the processor 502.

The network interface 504 can be used to enable the controller 500 tocommunicate on a network, such as to communicate control planeinformation to other controllers, to the management system 460, to aSoftware Defined Networking or OpenFlow controller, and the like. Thenetwork interface 504 can include, for example, an Ethernet card (e.g.,10BaseT, Fast Ethernet, Gigabit Ethernet) or a wireless local areanetwork (WLAN) card (e.g., 802.11a/b/g). The network interface 504 caninclude address, control, and/or data connections to enable appropriatecommunications on the network. The data store 506 can be used to storedata, such as control plane information, provisioning data, OAM&P data,etc. The data store 506 can include any of volatile memory elements(e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, and thelike)), nonvolatile memory elements (e.g., ROM, hard drive, flash drive,CDROM, and the like), and combinations thereof. Moreover, the data store506 can incorporate electronic, magnetic, optical, and/or other types ofstorage media. The memory 508 can include any of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)), nonvolatile memory elements (e.g., ROM, hard drive, flash drive,CDROM, etc.), and combinations thereof. Moreover, the memory 508 mayincorporate electronic, magnetic, optical, and/or other types of storagemedia. Note that the memory 508 can have a distributed architecture,where various components are situated remotely from one another, but maybe accessed by the processor 502.

The I/O interface 510 includes components for the controller 500 tocommunicate to other devices in a node, such as through the localinterface 514. The components (502, 504, 506, 508, 510) arecommunicatively coupled via a local interface 514. The local interface514 and the I/O interface 510 can be, for example but not limited to,one or more buses or other wired or wireless connections, as is known inthe art. The local interface 514 and the I/O interface 510 can haveadditional elements, which are omitted for simplicity, such ascontrollers, buffers (caches), drivers, repeaters, and receivers, amongmany others, to enable communications. Further, the local interface 514and the I/O interface 510 can include address, control, and/or dataconnections to enable appropriate communications among theaforementioned components.

The network element 12, the controller 500, and associated opticalnetworks and the like can utilized control plane systems and methods inaddition to or in replace of the standard management systemfunctionality. Control plane systems and methods provide automaticallocation of network resources in an end-to-end manner. Exemplarycontrol planes may include Automatically Switched Optical Network (ASON)as defined in G.8080/Y.1304, Architecture for the automatically switchedoptical network (ASON) (February 2005), the contents of which are hereinincorporated by reference; Generalized Multi-Protocol Label Switching(GMPLS) Architecture as defined in Request for Comments (RFC): 3945(October 2004) and the like, the contents of which are hereinincorporated by reference; Optical Signaling and Routing Protocol (OSRP)from Ciena Corporation which is an optical signaling and routingprotocol similar to PNNI (Private Network-to-Network Interface) andMPLS; or any other type control plane for controlling network elementsat multiple layers, and establishing connections there between. It isessential for the operation of control planes to have control planesignaling and Operations, Administration, Maintenance, and Provisioning(OAM&P) connectivity between nodes.

It is important to note that the one or more logical interfaces from themethods 100, 200, 300 are provided to the control plane and/ormanagement system for use thereof. In the control plane, the one or morelogical interfaces can be used for path computation, especially for meshreroutes in failure scenarios or for short-lived SNC or LSP requests.Thus, the systems and methods described herein provide the methods 100,200, 300 for determining and setting maximum bandwidths on flexibleoptical modems, the control plane and/or management system are madeaware of the excess capacity as one or more logical interfaces that areflagged as excess capacity, and collocated switching fabrics can usethese one or more logical interfaces at the direction of the controlplane and/or management system for various purposes such as restorationor short-lived SNCs or LSPs.

Hitless Modulation Change System

Referring to FIG. 8, in an exemplary embodiment, a block diagramillustrates a hitless modulation change system 600 at a node 12connected to an optical network 602. The node 12 includes one or moremodems 610, a fabric 620, and, optionally, one or more clienttransceivers 630. The modems 610 are flexible optical modems asdescribed herein, and interface optically via a bi-directionalconnection 635 to the optical network 602. The fabric 620 can include anoptical switching fabric (wavelengths), a time division multiplexing(TDM) fabric (OTN, SONET, SDH, etc.), and/or a packet switching fabric(Ethernet, MPLS, IP, etc.). Note, the fabric 620 can be implemented invarious different devices for different layers and/or in an integratedmanner. Here, in FIG. 8, the fabric 620 is shown as a single logicaldevice for illustration purposes. The fabric 620 is configured to switchwavelengths, channels, timeslots, tributary units, and/or packetsbetween and among the modems 610 as well as the client transceivers 630(note, in some exemplary embodiments, the client transceivers 630 may beomitted in the node 12). The client transceivers 630 are for localadd/drop of connections from the node 12.

The node 12 and the optical network 602 can include a control plane 640.Note, the connections formed through the fabric 620 between and amongthe modems 610 and/or the client transceivers 630 can be referred to asa data plane. The control plane 640 is a separate management plane tocontrol the connections in the data plane. Again, as described herein,the control plane 640 can include ASON, GMPLS, OSRP, etc., as well asother management mechanisms such as Software Defined Networking (SDN),Path Computation Element (PCE), and the like. That is, the control plane640 represents any mechanism for automatically allocating theconnections within the optical network 602 through the node 12.

As described herein, the node 12 and the modems 610, as flexible opticalmodems, support variable and flexible modulation schemes meant tomaximize optical capacity. For the hitless modulation scheme changesystems and methods, the node 12 includes or is communicatively coupledto a control agent 650 with the ability to probe the optical network 602to determine not only that a change is warranted and acceptable, butalso to determine the parameters of the impact of the traffic carryingcapability of the channels, and provide a mechanism to perform thechange without impacting traffic. Specifically, the control agent 650can be an autonomous system that coordinates between the modems 610 andthe fabric 620 to ensure that any modulation change in a particularmodem 610 is hitless to all underlying connections currently on themodem 610. This can be done through rerouting of the underlyingconnections via the fabric 620 and/or the control plane 640 during amodulation change process, and reverting the underlying connections backto the modem 610 subsequent to completion of the modulation changeprocess. In this manner, the modulation change process is hitless to theunderlying connections, the underlying connections are rerouted perexisting control plane behavior for restorations, and an end user doesnot have to manually manage the modulation change process.

The control agent 650 contemplates operation locally or remotelyrelative to the node 12. In an exemplary embodiment, the control agent650 is implemented in the controller 500. In another exemplaryembodiment, the control agent 650 is implemented in the managementsystem 450 or an SDN controller or application. Various otherembodiments are also contemplated. The control agent 650 iscommunicatively coupled to the modems 610, to the control plane 640, theSDN controller, the management system 450, and/or to the fabric 620. Thecontrol agent 650 can be configured to perform various functionsdescribed herein, such as determining a modulation change is warrantedand supported, determining the impact of the modulation change, causingrerouting of connections impacted by the modulation change, and thelike. That is, the control agent 650 implements an autonomousself-optimization of the modems 610 in the optical network 602.Importantly, the control agent 650 works with existing functionality inthe optical network 602 and the control plane 640, treating theunderlying connections as per standard restoration procedures while amodulation change occurs. In this manner, network behavior is preservedand the underlying connections are minimally impacted due to themodulation change (i.e., hitless based on the underlying restorationtechnique).

The approach contemplated herein can be referred to as a bottom-upapproach in that a modulation change is determined, and the controlagent 650 performs rerouting of the underlying connections first, withthe control plane 640, etc., prior to implementing the modulationchange. Thus, the modulation change can be implemented safely withoutimpacting the underlying connections, without adjustments at run-time,and without needing to minimize the length of the modulation change. Thecontrol agent 650 can be informed once the modulation change is completeand verified, and cause reversion of the underlying connections. Thecontrol agent 650 allows a bottom-up approach that is less complex(using existing functionality rather than adding extra functionality),is autonomous, and enables better temporal average spectral efficiencyof the modems 610 and the optical network 602. Additionally, the controlagent 650 can implement all or part of the methods 100, 200, 300described herein.

Hitless Modulation Change Method

Referring to FIG. 9, in an exemplary embodiment, a flow chartillustrates a hitless modulation change method 700 which can beimplemented through the control agent 650 in coordination with the modem610, the control plane 640, etc. The hitless modulation change method700 includes determining that a modulation change is needed on one ofthe modems 610 (step 702). This determination can be as describedherein, e.g. excess margin available, decrease in the margin, etc. Note,the hitless modulation change method 700 is described with reference toa single modem 610; however, the hitless modulation change method 700can be implemented concurrently for multiple modems 610 as required. Themodulation change includes going from a first modulation to a secondmodulation, and the either the first modulation or the second modulationcan provide more capacity, i.e. the modulation change can be an increaseor decrease.

The hitless modulation change method 700 includes determining the impactof the modulation change (step 704). The impact includes whichunderlying connections are affected by the modulation change, a lengthof time of the modulation change (either estimated or calculated), andthe like. Here, the hitless modulation change method 700 can determinewhich connections will be affected by the modulation change and abouthow long the modulation change will require. For example, the modem 610can report a length of time the modulation change will take, based onthe first modulation and the second modulation, link conditions, linemeasurements, etc.

Next, the hitless modulation change method 700 can cause rerouting ofany underlying connections which will be impacted by the modulationchange (step 706). Note, the hitless modulation change method 700 canalso support local buffering of data and retransmission subsequent tocompletion of the modulation change; however, this is likely complex andcostly due to the amount of bandwidth required. The hitless modulationchange method 700 can cause rerouting by alerting the control plane 640of which connections are affected, to allow the control plane 640 toreroute the connections per existing restoration techniques in theoptical network 602, and optionally, provide the length of time so thecontrol plane 640 could implement an automatic reversion. Thus, thehitless modulation change method 700 utilizes the control plane 640 tocoordinate a data path change in the data plane to accommodate themodulation change without interruption to the data flow.

Note, the rerouting of the underlying connections is per normalrestoration techniques which may include mesh restoration via thecontrol plane, 1+1/1:1 Automatic Protection Switching (APS), SubnetworkConnection Protection (SNCP), rings (BLSR, UPSR, etc.), G.8032 EthernetRing Protection Switching (ERPS) (ITU-T Recommendation G.8032/Y.1344(02/12) Ethernet ring protection switching, the contents of which areincorporated by reference herein), Virtual Local Area Network (VLAN)protection, and the like. That is, the control plane can use whatevertechniques are currently available in the data plane forrerouting/restoring connections in event of a fault. Here, themodulation change can be effectively viewed as a future fault that ismitigated in advance, ensuring no traffic impact.

However, a planned change in a channel path, in this case triggered bythe desire to change modulation formats, can be much less of a hit, interms of time, than a restoration/protection event driven by a failure.This is because the failure must be detected before the switch/re-routecan take place. By this time, it's already too late, so to speak—as datahas already been lost. In the case of a maintenance event, such as inthis use case, one can perform what is called a “bridge and roll” wherethe new path is brought up by duplicating the data across the new path.In this case, even a very simple switch can be used, in which case thedata which is “lost” is only due to the differential delay in the twopaths. It is also possible to adjust or align to the new path beforeswitching in which case there is no hit whatsoever. Thus, as describedherein, the modulation change is hitless or substantially hitless(traffic loss is only due to the differential delay in the two pathswhich is typically less than 50 ms).

Once all the underlying connections are accounted for, either byrerouting or buffering, the hitless modulation change method 700includes causing the modulation change (step 708). Here, the controlagent 650 can signal to the modem 610 that it can implement themodulation change. The hitless modulation change method 700 waits forthe modulation change to complete and verification (step 710). Note, itis expected the modulation change will take from about 1 s to multipleseconds. If there is a failure in the modulation change, the modem 610can revert back to the first modulation. If there is a success, themodem 610 will operate with the second modulation, and associatedcomponents in the modem 610 will adjust and normalize to the lineconditions with the second modulation (dispersion, non-linear effects,etc.). Once the second modulation is working, the modem 610 can verifysuccessful operation through various OAM&P parameters such as FEC.

With proper operation of the second modulation or reversion back to thefirst modulation, the hitless modulation change method 700 can includereversion of the underlying connections back to the modem 610 (step712). Here, the hitless modulation change method 700 can cause reversionor the underlying connections can automatically revert such as based onthe length of time plus a buffer time. Again, the entire hitlessmodulation change method 700 can be autonomous meaning it requires nouser intervention and it operates with existing data plane restorationfunctionality.

SDN Controller/Service for the Application

Referring to FIG. 10, in an exemplary embodiment, a block diagramillustrates a processing device 900 that can operate the control agent650. The processing device 900 can be a digital computer that, in termsof hardware architecture, generally includes a processor 902,input/output (I/O) interfaces 904, a network interface 906, a data store908, and memory 910. It should be appreciated by those of ordinary skillin the art that FIG. 10 depicts the processing device 900 in anoversimplified manner, and a practical embodiment may include additionalcomponents and suitably configured processing logic to support known orconventional operating features that are not described in detail herein.The components (902, 904, 906, 908, and 910) are communicatively coupledvia a local interface 912. The local interface 912 can be, for examplebut not limited to, one or more buses or other wired or wirelessconnections, as is known in the art. The local interface 912 can haveadditional elements, which are omitted for simplicity, such ascontrollers, buffers (caches), drivers, repeaters, and receivers, amongmany others, to enable communications. Further, the local interface 912can include address, control, and/or data connections to enableappropriate communications among the aforementioned components.

The processor 902 is a hardware device for executing softwareinstructions. The processor 902 can be any custom made or commerciallyavailable processor, a central processing unit (CPU), an auxiliaryprocessor among several processors associated with the processing device900, a semiconductor-based microprocessor (in the form of a microchip orchip set), or generally any device for executing software instructions.When the processing device 900 is in operation, the processor 902 isconfigured to execute software stored within the memory 910, tocommunicate data to and from the memory 910, and to generally controloperations of the processing device 900 pursuant to the softwareinstructions. The I/O interfaces 904 can be used to receive user inputfrom and/or for providing system output to one or more devices orcomponents. User input can be provided via, for example, a keyboard,touch pad, and/or a mouse. System output can be provided via a displaydevice and a printer (not shown). I/O interfaces 904 can include, forexample, a serial port, a parallel port, a small computer systeminterface (SCSI), a serial ATA (SATA), a fibre channel, Infiniband,iSCSI, a PCI Express interface (PCI-x), an infrared (IR) interface, aradio frequency (RF) interface, and/or a universal serial bus (USB)interface.

The network interface 906 can be used to enable the processing device900 to communicate on a network. The network interface 906 can include,for example, an Ethernet card or adapter (e.g., 10BaseT, Fast Ethernet,Gigabit Ethernet, 10 GbE) or a wireless local area network (WLAN) cardor adapter (e.g., 802.11a/b/g/n). The network interface 906 can includeaddress, control, and/or data connections to enable appropriatecommunications on the network. A data store 908 can be used to storedata. The data store 908 can include any of volatile memory elements(e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, and thelike)), nonvolatile memory elements (e.g., ROM, hard drive, tape, CDROM,and the like), and combinations thereof. Moreover, the data store 908can incorporate electronic, magnetic, optical, and/or other types ofstorage media. In one example, the data store 908 can be locatedinternal to the processing device 900 such as, for example, an internalhard drive connected to the local interface 912 in the processing device900. Additionally in another embodiment, the data store 908 can belocated external to the processing device 900 such as, for example, anexternal hard drive connected to the I/O interfaces 904 (e.g., SCSI orUSB connection). In a further embodiment, the data store 908 can beconnected to the processing device 900 through a network, such as, forexample, a network attached file server.

The memory 910 can include any of volatile memory elements (e.g., randomaccess memory (RAM, such as DRAM, SRAM, SDRAM, etc.)), nonvolatilememory elements (e.g., ROM, hard drive, tape, CDROM, etc.), andcombinations thereof. Moreover, the memory 910 can incorporateelectronic, magnetic, optical, and/or other types of storage media. Notethat the memory 910 can have a distributed architecture, where variouscomponents are situated remotely from one another, but can be accessedby the processor 902. The software in memory 910 can include one or moresoftware programs, each of which includes an ordered listing ofexecutable instructions for implementing logical functions. The softwarein the memory 910 includes a suitable operating system (O/S) 914 and oneor more programs 916. The operating system 914 essentially controls theexecution of other computer programs, such as the one or more programs516, and provides scheduling, input-output control, file and datamanagement, memory management, and communication control and relatedservices. The one or more programs 916 may be configured to implementthe various processes, algorithms, methods, techniques, etc. describedherein.

In an exemplary embodiment, processing device 900 can be configured toimplement the control agent 650. For example, the processing device 900can be an SDN controller or another device operating an SDN applicationin communication with the SDN controller. The processing device 900 canalso be a standalone device in communication with the various componentsin the hitless modulation change system 600. The SDN controller can alsoinclude an Application Programming Interface (API) which allowsadditional applications to interface with the SDN controller for dataassociated with the optical network 602. In an exemplary embodiment, thecontrol agent 650 can be implemented on the processing device 900 (or onthe processing device 900 operating as the SDN controller) and receivedata through the API. The processing device 900 can also be a standalonedevice in communication with the various components in the hitlessmodulation change system 600. Other configurations are alsocontemplated.

The processing device 900 can include a queue that performs the hitlessmodulation change method 700 on one or more of the modems 610. Again,the hitless modulation change systems and methods contemplate operationof the hitless modulation change method 700 for one or more of themodems 610 simultaneously, as appropriate. For example, the modems 610can be managed based on location in the optical network 602 along withappropriate rules. One exemplary rule may be that only one modem 610 ata time in a node 12 can perform the hitless modulation change method700, whereas modems 610 in different nodes 12 can perform concurrently.Also, of note, the hitless modulation change method 700 is performed atboth ends of a connection simultaneously. The control agent 650 can be alocal device that communicates with a peer control agent 650 tocoordinate the modulation change. Alternatively, the control agent 650can have a global view and perform both ends simultaneously, for anoptical section.

It will be appreciated that some exemplary embodiments described hereinmay include one or more generic or specialized processors (“one or moreprocessors”) such as microprocessors, digital signal processors,customized processors, and field programmable gate arrays (FPGAs) andunique stored program instructions (including both software andfirmware) that control the one or more processors to implement, inconjunction with certain non-processor circuits, some, most, or all ofthe functions of the methods and/or systems described herein.Alternatively, some or all functions may be implemented by a statemachine that has no stored program instructions, or in one or moreapplication specific integrated circuits (ASICs), in which each functionor some combinations of certain of the functions are implemented ascustom logic. Of course, a combination of the aforementioned approachesmay be used. Moreover, some exemplary embodiments may be implemented asa non-transitory computer-readable storage medium having computerreadable code stored thereon for programming a computer, server,appliance, device, etc. each of which may include a processor to performmethods as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, an optical storage device, a magnetic storage device, a ROM(Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM(Erasable Programmable Read Only Memory), an EEPROM (ElectricallyErasable Programmable Read Only Memory), Flash memory, and the like.When stored in the non-transitory computer readable medium, software caninclude instructions executable by a processor that, in response to suchexecution, cause a processor or any other circuitry to perform a set ofoperations, steps, methods, processes, algorithms, etc.

Although the present disclosure has been illustrated and describedherein with reference to preferred embodiments and specific examplesthereof, it will be readily apparent to those of ordinary skill in theart that other embodiments and examples may perform similar functionsand/or achieve like results. All such equivalent embodiments andexamples are within the spirit and scope of the present disclosure, arecontemplated thereby, and are intended to be covered by the followingclaims.

What is claimed is:
 1. A hitless modulation change method at a node inan optical network, the hitless modulation change method comprising:determining that a modulation change from a first modulation scheme to asecond modulation scheme is warranted for an optical modem in the node,the optical modem configured to communicate over an optical link;determining an impact of the modulation change on the optical link andassociated underlying connections thereon comprising determining alength of time the modulation change will take based on a type of themodulation change and conditions on the optical link; causing changes ina data plane for the associated underlying connections, prior toperforming the modulation change; and causing the modulation changesubsequent to accommodating the associated underlying connections in thedata plane, thereby minimizing interruptions of the associatedunderlying connections due to the modulation change.
 2. The hitlessmodulation change method of claim 1, further comprising: causingreversion of the associated underlying connections to the optical linksubsequent to completion and verification of the modulation change. 3.The hitless modulation change method of claim 1, wherein the causingchanges in the data plane utilizes a control plane and restoration ofthe associated underlying connections per normal control plane behavior.4. The hitless modulation change method of claim 3, wherein the normalcontrol plane behavior comprises any of mesh restoration via the controlplane, 1+1/1:1 Automatic Protection Switching (APS), SubnetworkConnection Protection (SNCP), ring restoration, G.8032 Ethernet RingProtection Switching (ERPS), and Virtual Local Area Network (VLAN)protection.
 5. The hitless modulation change method of claim 1, whereinthe length of time is communicated with the changes in the data planefor the associated underlying connections.
 6. The hitless modulationchange method of claim 1, wherein the determining steps and the causingsteps are performed by a control agent communicatively coupled to thenode.
 7. The hitless modulation change method of claim 6, wherein thecontrol agent operates in an autonomous manner and communicates withexisting control plane functionality associated with the node to causethe changes in the data plane.
 8. A hitless modulation change systemcommunicatively coupled to a node in an optical network, the hitlessmodulation change system comprising: a processor; and memory storinginstructions that, when executed, cause the processor to determine thata modulation change from a first modulation scheme to a secondmodulation scheme is warranted for an optical modem in the node, theoptical modem is configured to communicate over an optical link,determine an impact of the modulation change on the optical link andassociated underlying connections thereon comprising determining alength of time the modulation change will take based on a type of themodulation change and conditions on the optical link, cause changes in adata plane for the associated underlying connections, prior toperforming the modulation change, and cause the modulation changesubsequent to accommodating the associated underlying connections in thedata plane, thereby minimizing interruptions of the associatedunderlying connections due to the modulation change.
 9. The hitlessmodulation change system of claim 8, wherein the memory storinginstructions that, when executed, further cause the processor to: causereversion of the associated underlying connections to the optical linksubsequent to completion and verification of the modulation change. 10.The hitless modulation change system of claim 8, wherein the changes inthe data plane are caused utilizing a control plane and restoration ofthe associated underlying connections per normal control plane behavior.11. The hitless modulation change system of claim 10, wherein the normalcontrol plane behavior comprises any of mesh restoration via the controlplane, 1+1/1:1 Automatic Protection Switching (APS), SubnetworkConnection Protection (SNCP), ring restoration, G.8032 Ethernet RingProtection Switching (ERPS), and Virtual Local Area Network (VLAN)protection.
 12. The hitless modulation change system of claim 8, whereinthe length of time is communicated with the changes in the data planefor the associated underlying connections.
 13. The hitless modulationchange system of claim 8, wherein the hitless modulation change systemis implemented through or communicatively coupled to a Software DefinedNetworking (SDN) controller.
 14. The hitless modulation change system ofclaim 8, wherein the hitless modulation change system operates in anautonomous manner and communicates with existing control planefunctionality associated with the node to cause the changes in the dataplane.
 15. An optical node implementing hitless modulation changes in anoptical network, the optical node comprising: one or more opticalmodems; a fabric coupled to the one or more optical modems for switchingof connections; and a processing device implementing a control agent,wherein the control agent is configured to determine that a modulationchange from a first modulation scheme to a second modulation scheme iswarranted for an optical modem in the node, the optical modem isconfigured to communicate over an optical link, determine an impact ofthe modulation change on the optical link and associated underlyingconnections thereon comprising determining a length of time themodulation change will take based on a type of the modulation change andconditions on the optical link, cause changes in a data plane for theassociated underlying connections through the fabric, prior toperforming the modulation change, and cause the modulation changesubsequent to accommodating the associated underlying connections in thedata plane, thereby minimizing interruptions of the associatedunderlying connections due to the modulation change.
 16. The opticalnode of claim 15, wherein the changes are caused in the data planeutilizing a control plane and restoration of the associated underlyingconnections per normal control plane behavior with the fabric.
 17. Theoptical node of claim 15, wherein the control agent is configured tocause reversion of the associated underlying connections to the opticallink subsequent to completion and verification of the modulation change.18. The optical node of claim 17, wherein the normal control planebehavior comprises any of mesh restoration via the control plane,1+1/1:1 Automatic Protection Switching (APS), Subnetwork ConnectionProtection (SNCP), ring restoration, G.8032 Ethernet Ring ProtectionSwitching (ERPS), and Virtual Local Area Network (VLAN) protection. 19.The optical node of claim 15, wherein the length of time is communicatedwith the changes in the data plane for the associated underlyingconnections.
 20. The optical node of claim 15, wherein the control agentoperates in an autonomous manner and communicates with existing controlplane functionality associated with the optical node to cause thechanges in the data plane.